The present invention relates generally to systems for cooling lubricating oil in internal combustion engines, and more particularly, to an air cooled engine oil cooler for use in a pressure lubricated, internal combustion engine.
In air cooled internal combustion engines, and in particular, in single cylinder die cast aluminum air cooled engines of the type having a pressure lubrication system and a vertically-oriented crankshaft, the temperature of the lubricating oil is higher than in liquid cooled engines. For example, when an air cooled engine having an enclosed or restricted cooling air flow is used in ambient air temperatures in excess of 100.degree. F., the temperature of the engine lubricating oil may exceed 300.degree. F. under normal operating conditions. At this temperature, the lubricating oil will rapidly oxidize and break down. This may result in excessive engine wear and premature engine failure due to the lack of lubrication. In order to prevent such excessive engine wear, it is generally preferred that the temperature of the lubricating oil not exceed 220.degree. F. under normal operating conditions.
Prior art lubricating oil coolers that have been utilized with large and brute cylinder air cooled engines have generally used a finned tube type of heat exchanger within the cooling air ductwork and shroud of the engine air cooling system. This type of heat exchanger has been found effective in reducing the lubricating oil temperature of the air cooled engine, however, the cost and complexity of installation of this type of system make it impractical for use in small, relatively low-cost, single cylinder internal combustion engines of the type used in lawn mowers and the like.
Another technique for cooling engine lubricating oil is disclosed in U.S. Pat. No. 4,607,601. With this technique, oil flows under the influence of gravity in a generally downward direction through a series of cascade ribs arranged in a staggered pattern on the inside surface of a timing gear cassette housing. The staggered ribs are arranged to provide a circuitous cooling flow path for the oil as it returns to the sump. External ribs are provided on the outside of the housing for additional cooling. Although this system provides an effective technique for cooling lubricating oil, the system is limited in that it is entirely dependent upon conduction and radiation for heat transfer. No forced convection heat exchange is utilized. This system is applied to those engines wherein lubricating oil returns to the sump by gravity. It is not generally useful in engines utilizing a pressure lubrication system.
It is desired to provide an engine oil cooler for a pressure lubricated internal combustion engine that is low in cost, and that is effective in cooling the engine lubricating oil to a temperature below that which would cause the oil to rapidly oxidize and break down.